Personal computers, portable transmitters, personal information processor, etc., process text and graphics data using an input apparatus such as a keyboard, a mouse or a digitizer.
The digitizer is for digitally detecting the position of a pen or a finger on a flat panel specifically manufactured to output X and Y coordinates of the position and has merits in that characters and figures both can be input easily and accurately in comparison to a conventional mouse, keyboard or scanner. Further, the digitizer is envisioned to replace the conventional input devices.
The digitizer is classified into three types: a stylus type using a specially devised pen; a finger touch type using a finger; and a touch panel type using a common pen or any pointed object.
The stylus type is widely used in graphics or CAD applications. The finger touch type is used in an apparatus adopting a touch screen display. The touch panel type is used in a personal digital assistance (PDA) or an electronic organizer.
To implement a digitizer system, a tablet for assigning coordinate data, a pointing device such as a stylus, a pen or a finger for locating a position on a coordinate system represented by the tablet, and a digitizer controller for controlling the above elements.
The tablet has a specially manufactured rectangular panel. The panel is coated with a resistive film for the stylus type or the finger touch type or is constituted by two sheets of resistive material separated by a spacer and concurrently arranged to be capable of contact by pressure for the touch panel type.
The location of the pointing device is recognized by the differences in detected signals according to the pressed position when an AC (the stylus and the finger touch types) or DC (the touch panel type) signal is applied at the four corners of the panel. Such a panel and controller are disclosed in U.S. Pat. Nos. 4,600,807, 4,649,232, 4,650,962 and 4,665,283, thus a description thereof will be omitted.
However, since the conventional digitizer controller is specifically designed for only one of the three types described above, it is inconvenient to equip a corresponding digitizer controller according to each type. Also, since the digitizer controller is embodied with discrete circuit elements, the size of the apparatus becomes large and power consumption is high.